The present invention relates to a method and apparatus for tracking relative to time the performance, reliability and condition of line replacement units used on aircraft and other types of machines.
Auxiliary power units (APU) for aircraft may generally be gas turbine engines used on aircraft to supply pneumatic power and/or shaft horsepower when the primary propulsion engines may not be operating. Typically, as illustrated in FIG. 1, the APU 10 may be mounted in the tailcone 12 of the aircraft, though on some airplanes such as the Boeing 727, the APU may be mounted in the wheel well.
Referring to FIG. 2, one form of an auxiliary power unit to which the present invention relates may generally be denoted by reference numeral 10. The APU 10 may include in flow series arrangement a compressor inlet 14, a compressor 16, a bleed port 18 for providing compressed air to the aircraft, a combustor 20 having a primary fuel nozzle 22 and a secondary fuel nozzle 24, a turbine 26 and a gas exhaust 28. The compressor 16 and the turbine 26 may be mounted for rotation on a shaft 30 that extends to and drives a gearbox 32. Mounted to the gearbox 32 may be accessory components such as an electric generator 34, a lube pump 36, a fuel control unit 38 and a start motor 40. When one of these components fails, it may be easily removed by detaching it from the gearbox 32 and replacing it with a new component that may be just as easily attached to the gearbox 32. In many instances, these components may be attached/detached without removing the APU from the aircraft. For some configurations in order to attach/detach these components, the APU may have to be removed from the aircraft. In these cases, however, the replacing of the components may occur on the tarmac adjacent the aircraft. In either scenario, the component may be replaced without removing the aircraft from operation. Accordingly, these components are referred to as Line Replaceable Units, (LRU), as they can be replaced without taking the aircraft out of operation or off line.
In operation, as the shaft 30 rotates, air may be inducted through the inlet 14 and pressurized in the compressor 16. Any required bleed air flows through bleed port 18 with the remaining air flowing into the combustor 20. In the combustor 20 the air may be mixed with fuel and ignited to form a hot pressurized gas. This gas expands across the turbine 26, causing the turbine 26, shaft 30, compressor 16 and gearbox 32 input to rotate which in turn drives the LRUs 34, 36, 38 and 40. The expanded gas then flows through the exhaust 28 and out into the surrounding environment. The operation of the APU 10 is controlled by an electronic control unit (ECU), not shown, that may be remotely located from the APU 10 in the aircraft.
The APU has a data memory module (DMM) that collects and stores APU operational and performance data as well as the serial number of the APU. This data may be used for tracking the APU health and operational conditions. Some life cycle calculations may be made by the ECU and stored in the DMM. Data is manually collected from the DMM when the aircraft may be taken off line and into a repair and overhaul facility.
For cost and performance reasons, the ability to track the performance, reliability and condition of these LRUs may be important. However, these types of components may be very difficult to track in the field. The LRUs may often be replaced, exchanged, or even discarded when thought to have failed.
Current systems use the data stored in the DMM to try to predict the failure of LRUs by evaluating performance trends (trending) of the APU as a whole. However, trending the LRUs as part of the APU has not been very successful, as current systems do not account for or know a units current configuration. That is they do not have a way to detect when an old LRU has been replaced with a new LRU. Current trending systems look at operational parameters to track particular performance trends looking for changes over time. Current systems fall short when an LRU may be replaced because the new LRU will affect the APU performance trend. Although the data in the DMM may show a change in APU performance, it may not be evident why the performance data has changed. Currently, there is no way for the current trending systems to know that an LRU has been changed. In addition, current systems do not use trend monitoring for the individual LRU components.
As can be seen, there is a need for a trending system and method that is able to determine the exact configuration of the APU as well as provide a method for each of the LRUs to be individually trended.
Although the foregoing description pertains to the use of this invention for APUs, similar application and benefits exist for LRUs associated with propulsion gas turbine engines and other machines.